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Synopsis: La Niña has transitioned to ENSO-neutral conditions, which are expected to continue through northern summer 2012.

La Niña dissipated during April 2012, as below-average SSTs weakened across most of the equatorial Pacific Ocean and above-average SSTs persisted in the east (Fig. 1). The Niño 4 and Niño 3.4 indices were warmer than -0.5^oC throughout the month, and the Niño 3 and Niño 1+2 indices remained positive (Fig. 2). The oceanic heat content (average temperature in the upper 300m of the ocean) anomalies also became positive in April (Fig. 3), as below-average sub-surface temperatures largely disappeared and above-average sub-surface temperatures expanded in both the central and eastern Pacific (Fig. 4). Consistent with the demise of La Niña, enhanced trade winds and reduced convection over the central equatorial Pacific were much weakened during April, and the area of enhanced convection that had previously dominated the western Pacific and Indonesia became disorganized (Fig. 5). Collectively, these oceanic and atmospheric patterns indicate a transition from La Niña to ENSO-neutral conditions. (more…)

There is no doubt the La Niña has returned. Check out the Pacific Ocean temperature anomalies in this image from NOAA’s Environmental Visualization Laboratory.

A sea surface anomaly, or departure from the average temperature, is calculated by subtracting the temperatures from a time period of interest from the 30-year average (1981-2010) for the same time period. The resulting data shows areas that are hotter or colder than normal. Sea surface temperature anomaly data allow scientists to quickly identify features of interest, especially for El Niño/La Niña, coastal upwelling, and hurricane intensification.

The strengthening La Niña in the Pacific Ocean brings with it a host of possible trends as outlined by the NOAA Climate Prediction Center’s Seasonal Outlook released October 20, 2011. These trends include lower than normal precipitation for the southwest and southern Great Plains and Mississippi Valley. Below normal temperatures are favored for southern sections of the Florida peninsula, northern Great Plains and northern Rockies. Trends favor modest warmer than normal conditions for much of the east.

Unfortunately for Central Texas and most of the state, this means a continuation of our historic drought into 2012.

This imagery uses the Optimum Interpolation SST (commonly called OI SST) anomaly dataset generated by NOAA’s National Climatic Data Center. OI SST uses infrared and microwave data from polar-orbiting satellites (NOAA AVHRR; NASA AMSR-E, a previous contributor operating onboard the AQUA satellite, ceased operation October 4, 2011) and oceanic buoys to calculate one of the most accurate analyses of sea surface temperature.

Related Information:NOAA/NCDC OI SST products page

(Content from NOAA)

Our monthly La Niña update from the Climate Prediction Center indicates a weakening phase has begun, but the cooler-than-average Pacific water temperatures will likely remain an influence in our weather into, and possibly through spring.  Most notably, below average rainfall is expected across Texas, which will worsen our ongoing drought conditions.

While the rainfall since yesterday has been a welcome change, don’t get used to it.  In an ominous sign from the Climate Prediction Center today, experts say they are interpreting the current cooling of some areas of the Pacific Ocean to be a sign that a La Nina is in the process of developing, and should fully form over the summer. 

La Nina episodes are normally responsible for bringing drier than average weather to Texas. A persistent La Nina period helped create our area’s record breaking drought between 2007-2009.  In other words, our next drought may be beginning now.

In today’s monthly update from the Climate Prediction Center, some mixed news for us as we head closer to summer. 

Climate forecasters are predicting drier than average weather in the 8-14 day period, which takes us into early June (see graphic below).  That would not be good news, as we have yet to see normal May rainfall.  Only one inch of rain has fallen so far this month at the airport, which is about two inches below average.

There is better news when looking at the CPC’s June outlook (below). Our Central Texas  region is in, or near the area forecast to receive above average rainfall during the month of June.

And, I don’t think anyone will complain about the temperature outlook below. Notice that nearly all of  Texas is forecast to be cooler than normal during June. Let’s hope that is right!

And while not quite as optimistic of an outlook for our area, notice below that parts of Central Texas are in the region of the state forecast to experience a cooler-than-normal summer.

 In the graphics below, most of North Texas is expected to enjoy below average temperatures during the period June through August, but most of the state, except the upper Texas coast,  has an equal chance of being wetter or drier than normal.

Read the CPC’s climate discussions below, where they pronounce the end of the El Nino, and discuss increasing evidence that a La Nina episode may be returning this year.

PROGNOSTIC DISCUSSION FOR MONTHLY OUTLOOK
NWS CLIMATE PREDICTION CENTER CAMP SPRINGS MD
830 AM EDT THU MAY 20 2010

30-DAY OUTLOOK DISCUSSION FOR JUNE 2010

SEA SURFACE TEMPERATURE (SST) ANOMALIES NEAR THE EQUATOR IN THE EAST CENTRAL
PACIFIC OCEAN HAVE DECREASED MARKEDLY IN THE PAST FEW WEEKS.  SSTS ARE NOW
SLIGHTLY BELOW NORMAL ALONG THE EQUATOR BETWEEN ABOUT 100 AND 160W LONGITUDE,
SUGGESTING AN END TO THE EL NINO CONDITIONS PRESENT FOR THE PAST YEAR OR SO.
SEVERAL

(more…)

The Climate Prediction Center’s monthly update today was a little discouraging.  We already knew the El Nino was fading away.  We owe our drought-breaking fall and winter rainfall to the pattern, so it’s hard to say goodbye, but that’s the nature of this cyclical pattern. 

One would hope that we would at least transition to a period of “neutral” or average Pacific Ocean water temperatures for the remainder of the year, which is likely. However, the CPC said today that a third of their climate models are predicting a quick transition to a La Nina pattern. 

That, of course, would be bad news for us, as much of the credit, or blame, for our record breaking two year drought was given to a persistent La Nina weather pattern.